1. Field of the Invention
The present invention relates to a catalyst temperature estimating apparatus for estimating the catalyst temperature installed in the exhaust system of an internal combustion engine, and particularly relates to a catalyst temperature estimating apparatus capable of estimating the catalyst temperature even when the internal combustion engine is stopped.
2. Background Art
Recently, in order to improve fuel consumption and to reduce the emission of noxious components, an automatic starting and stopping apparatus has been proposed, which automatically stops the engine under certain driving conditions, and automatically starts the engine when the driver conducts a starting operation of the vehicle. An example of this automatic starting and stopping apparatus stops the engine when the engine is in idling operation, and the brake pedal is depressed, and the shift position of the transmission is at neutral position, and the vehicle speed is zero (hereinafter, this engine stop state is called as idle stop).
Particularly, in the case of a hybrid vehicle provided with an electric motor together with an internal combustion engine as the driving power sources of the vehicle, since the internal combustion engine can be driven by the motor installed in the vehicle, the internal combustion engine once stopped can be restarted easily, and such an idle stop operation is adopted for hybrid vehicles.
In order to provide compatibility of protecting the catalyst installed in the exhaust system of the internal combustion engine and preserving the low fuel consumption rate, for example, Japanese Unexamined Patent Application, First Publication No. Hei 10-205375 proposes an apparatus to estimate the temperature of the catalyst installed in the exhaust system of the internal combustion engine and increases fuel supply when the load becomes high. However, the apparatus disclosed in the above Japanese Unexamined Patent Application, First Publication No. Hei 10-205375 estimates that the temperature of the catalyst became sufficiently lower and sets the estimated temperature to an initial value when the engine is stopped and restarted.
However, when the above-described conventional apparatus is applied to hybrid vehicles having the idle stop function, the estimated catalyst temperature is set at the low initial catalyst temperature even when the engine is restarted before the catalyst temperature falls to the level of the low initial temperature. As a result, the problems arise that the estimated catalyst temperature includes an error and that it takes time for the estimated temperature to catch up the actual catalyst temperature.
It is therefore an object of the present invention to provide a catalyst temperature estimating apparatus of the internal combustion engine, which carries out estimation of the catalyst temperature at every predetermined intervals by further providing parameters for calculating the catalyst temperature during the idle stop operation.
In order to attain the above object, a catalyst temperature estimating apparatus of the present invention comprises a driving state detection device (in the embodiment, the absolute pressure sensor 8 in an intake pipe, the engine coolant temperature sensor 10, the crank angle sensor 11, etc.) for detecting a driving state of an internal combustion engine (in the embodiment, the engine 1), a catalyst (in the embodiment, the three way catalyst 15) installed in the exhaust system (in the embodiment, the exhaust pipe 14) of the internal combustion engine, a temperature estimation apparatus (in the embodiment, step S19) for estimating a temperature of the catalyst based on the output of the driving state detecting device, and a determination device for determining whether the internal combustion engine is operating or stopping, wherein the temperature estimating device estimates the temperature of the catalyst based on predetermined values (in the embodiment, TCTMIS and CTCTIS) used at the time of the engine stop when it is determined by the determination device that the internal combustion engine is stopping.
Furthermore, the catalyst temperature estimating apparatus according to the first aspect is capable of executing an idle stop.